Field of the Invention
The present disclosure relates generally to an optical coupler array for coupling, e.g., a plurality of optical fibers to at least one optical device. Some embodiments can relate generally to high power single mode laser sources, and to devices for coherent combining of multiple optical fiber lasers to produce multi-kilowatt single mode laser sources. Some embodiments may relate to phase locked optical fiber components of a monolithic design that may fabricated with a very high degree of control over precise positioning of even large quantities of plural waveguides, and that may potentially be configurable for increasing or optimization of the components' fill factor (e.g., of the ratio of the mode field diameter of each waveguide at the “output” end thereof, to the distance between neighboring waveguides). The optical fiber array can be a polarization maintaining optical fiber array that can orient or control the orientation of the polarization axes of individual optical fibers (e.g., permit alignment of all polarization axes of individual optical fibers of the components in some instances) without the need for adjustment of orientation of individual fibers.
Description of the Related Art
Optical waveguide devices are useful in various high technology industrial applications, and especially in telecommunications. In recent years, these devices, including planar waveguides, and two or three dimensional photonic crystals are being employed increasingly in conjunction with conventional optical fibers. In particular, optical waveguide devices based on high refractive index contrast or high numerical aperture (NA) waveguides are advantageous and desirable in applications in which conventional optical fibers are also utilized. However, there are significant challenges in interfacing optical high NA waveguide devices, including chiral optical fiber devices, with conventional low index contrast optical fibers. For example, in some cases, at least two major obstacles may be encountered: (1) the difference between the sizes of the optical waveguide device and the conventional fiber (especially with respect to the differences in core sizes), and (2) the difference between the NAs of the optical waveguide device and the conventional fiber. Failure to properly address these obstacles can result in increased insertion losses and a decreased coupling coefficient at each interface.
For example, conventional optical fiber based optical couplers, such as shown in FIG. 6 (Prior Art) can be configured by inserting standard optical fibers (used as input fibers) into a capillary tube comprised of a material with a refractive index lower than the cladding of the input fibers. However, there are a number of disadvantages to this approach. For example, a fiber cladding-capillary tube interface becomes a light guiding interface of a lower quality than interfaces inside standard optical fibers and, therefore, can be expected to introduce optical loss. Furthermore, the capillary tube must be fabricated using a costly fluorine-doped material, greatly increasing the expense of the coupler.
U.S. Pat. No. 7,308,173, entitled “OPTICAL FIBER COUPLER WITH LOW LOSS AND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF”, which is hereby incorporated herein in its entirety, advantageously addressed issues discussed above by providing various embodiments of an optical fiber coupler capable of providing a low-loss, high-coupling coefficient interface between conventional optical fibers and optical waveguide devices.
Nevertheless, a number of challenges still remained. With the proliferation of optical devices with multiple waveguide interfaces (e.g., waveguide arrays), establishing low-loss high-accuracy connections to arrays of low or high NA waveguides often was problematic, especially because the spacing between the waveguides is very small making coupling thereto all the more difficult. U.S. Pat. No. 8,326,099, entitled “OPTICAL FIBER COUPLER ARRAY”, issued Dec. 4, 2012, which is hereby incorporated herein by reference in its entirety, endeavors to address the above challenge by providing, in at least a portion of the embodiments thereof, an optical fiber coupler array that provides a high-coupling coefficient interface with high accuracy and easy alignment between an optical waveguide device having a plurality of closely spaced high NA waveguide interfaces, and a plurality of optical fibers each having low numerical apertures separated by at least a fiber diameter.
U.S. Patent Application Publication No. 2013/0216184, entitled “CONFIGURABLE PITCH REDUCING OPTICAL FIBER ARRAY,” which is expressly incorporated by reference herein, teaches a pitch reducing optical fiber array (“PROFA”) coupler/interconnect using a vanishing core approach. In at least some of the example implementations thereof, the tip of the PROFA component can be butt-coupled to a photonic integrated circuit (“PIC”), an array of vertical grating couplers (“VGCs”), or delivers the light to free-space optics. Improved coupling to two-dimensional (“2D”) polarization maintaining fiber arrays with control of the orientation of the polarization axes can be desirable.